In numerous environments, electronic instruments and systems are used for the measurement of parameters important in that environment. For example in developmental laboratories and in manufacturing facilities, electronic instruments can be used to measure the thicknesses of parts, machine alignments, signal frequencies, dielectric constants, optical parameters, etc. To ensure that the values obtained in these measurements are accurate, the instruments involved must be periodically calibrated.
For some companies, the accurate calibration of their instruments is so important that they employ a calibration system in which the calibration history of each instrument is centrally maintained. Further, the accuracy of the standards used in the calibration of the instruments are traceable to the National Institute of Standards and Technology. In some cases, the traceable standards used are maintained by the company""s standards laboratory. To be National Institute of Standards and Technology traceable, there must be an unbroken chain of measurements from the instrument calibration to standards which are maintained by the National Institute of Standards and Technology.
Based on the calibration history of a particular instrument, the instrument may be physically removed from service, which could be a production floor, for calibration. Depending upon the timing of the calibration and the amount of time needed to perform the calibration, the removal of a particular instrument from active service may prevent the manufacturing operation from making a needed measurement or measurements in a timely manner. The lack of such a measurement or measurements may result in the manufacturing process drifting out of specification or alternatively a production line may be temporarily shut down until such calibration is completed.
Different companies maintain calibration programs with various degrees of success. At one end of the spectrum, some companies maintain very rigid, accurate calibration programs which are centrally controlled. When a particular instrument should be calibrated may be determined from a computer database. In other cases, a removable sticker which lists the calibration due date may be placed on the instrument. At the other extreme, other companies may seldom, if ever, perform calibrations. Even when calibrations are performed, it may be that they are completed against standards that are not traceable to the National Institute of Standards and Technology. Some companies may initiate comprehensive calibration programs but, with time, become overwhelmed by the complexity of maintaining the timely calibration of what may number in the hundreds of instruments.
In a representative embodiment, a method includes determining instrument calibration status, wherein the determination is made automatically by the instrument examining calibration history data stored by the instrument. When instrument calibration is past due, a user is notified that the calibration is past due, wherein the notification is initiated automatically by the instrument. The user can decide to make the measurement with the out-of-calibration instrument. Otherwise, the instrument is removed from measurement service, the instrument is calibrated, the calibration history stored by the instrument is updated to reflect a new time that a new calibration is due, and the instrument is returned to measurement service. Additionally, when the instrument calibration due date is approaching, a user may be notified of that fact automatically by the instrument. Also described are techniques for calibrating only those signal paths, subsystems, and ranges are actually being used or may potentially be used. In addition, if the user does decide to make a measurement while the instrument is out of calibration, he may be informed of the measurement uncertainty in making such a measurement.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.